Recent studies have focused on the potential value of nutritional support to the patient with neoplastic disease. Concomitantly, there has been increased interest in the anorexia-cachexia syndrome in patients with cancer, a syndrome in which patients, with, at times, early tumors, manifest weight loss secondary to reduced intake out of proportion to their tumor burden. One of the theories of the etiology of this syndrome is that certain metabolic changes brought about by the tumor affect the central "appetite-satiety center" in such patients. Recent neurophysiological studies have focused attention on the appetite-satiety center, so called, as perhaps involving indoleamine (serotonin) and catecholamine (norepinephrine, dopamine neurotransmitters. The proposed studies are related to the hypothesis, supported by preliminary experiments, that in animals with implanted Walker-256 carcinosarcoma tumors, anorexia, in an early manifestation is causally related to increased synthesis of brain serotonin. Studies are addressed to the nature of the alterations in the metabolism of tryptophan, tyrosine and phenylalanine, precursors of these neurotransmitters, and factors controlling their penetration across the blood-brain barrier, including plasma free and total tryptophan, non-esterified fatty acids, plasma neutral amino acid ratios, serum albumin, etc. If these hypotheses prove correct, manipulation of the plasma concentrations of free or total tryptophan or other members of the competing large neutral amino acid group, or the administration of central serotonin antagonists, may prevent the development of anorexia. Similar studies measuring plasma free and total tryptophan as well as plasma amino acid patterns will be carried out in patients with anorexia in the presence of neoplastic disease and following therapy when anorexia is no longer present. Since malnutrition is an important cause of moribidity and mortality in patients with neoplastic disease, prevention of such malnutrition, by manipulation of central neurotransmitters may be of immense value to patients with cancer.